In a typical camera lens barrel, an outer diameter of the lens is relatively large. Therefore, the flange portion of the lens is held with tweezers and the lens is dropped into the lens frame to manufacture the lens barrel. Instead of using tweezers, air is sucked to adsorb the lens with an adsorption pad to hold the lens.
In a lens barrel composing a tip portion of an endoscope with a small diameter of about 1 mm, when the lens frame is a small diameter or the lens frame is long in an optical axis direction (therefore, the lens inserting hole is deep), it is difficult to insert the lens. Undoubtedly, using tweezers to hold such a very small lens is very difficult, and accurately inserting the lens into the lens frame by free fall is also very difficult.
An endoscope is used to be inserted in a live body lumen to observe live body tissue. As a structure of a tip of the endoscope, there is a structure providing a lens which images an image of an object of an observation target and an imaging element or an imaging fiber such as a CCD (charge coupled device) in which the image is input. When the imaging element is used, an image signal converted to an electric signal with the imaging element is transmitted outside the body with a transmitting cable, and when the imaging fiber is used, the image is transmitted outside the body with the imaging fiber as is, and after going through the image processing apparatus, the image can be displayed and observed on the image display apparatus.
As described in patent literature 1 to 5, the lens is positioned inside the lens frame and the outer circumferential portion of the lens is adhered to the inner circumferential surface of the lens frame to fix the units in order to include the lens in the optical device. When the lens is fixed with adhesive, it is important that a sufficient amount of adhesive can be filled in the necessary portion and that the adhesive is not attached to the optical surface of the lens so that there is no bad influence to the optical performance.
According to patent literature 1 to 3, a ring shaped groove is provided to prevent the adhesive from flowing out to the effective face of the lens. The ring shaped groove is provided in the lens and one or both holding planes.
According to patent literature 4, in order to prevent the lens from rising in the thrust direction, a tapered portion is provided in the lens or the inner circumferential portion of the frame and the portion is filled with adhesive. The hardening shrinkage of the adhesive causes pulling force in the thrust direction.
According to patent literature 5, a through hole is provided to insert adhesive in a gap between the lens supporting frame and the lens circumferential surface.
Patent literature 6 and 7 describe a tip structure of an endoscope in which the lens and the imaging fiber are positioned on the same axis and fixed with a cylinder shaped frame.